(x+y-z)(x-y+z)=(x+(y-z))(x-(y-z))=x^2-(y-z)^2=x^2-y^2+2yz-z^2
(x+y-z)(x-y+z)=x²-(y-z)²=x²-(y²-2yz+z²)=x²-y²+2xy-z²
